Life Cycle Emissions - Current Decade. Substitution of materials, equipment and low carbon fuels for high carbon fuels is underway and moving forward faster in some countries and economic sectors than others. Substitution of manufactured equipment for fuels adds “life cycle carbon” to historical and on-going GHG emissions. To what extent do GHGs emitted in creating low carbon energy economies retard overall decarbonization progress? The table below shows estimated global energy equipment life cycle GHG (“carbon”) emissions for key energy technologies that enable energy sector decarbonization. Life cycle carbon emissions for the years 2020 through 2029 add up to a minimum of 35 billion metric tons of CO2-eq, or roughly a year’s worth of current global energy related GHG emissions. Overall life cycle carbon emissions will continue to increase after 2029 at least until direct global GHG emissions are brought under control.
Estimated Global Energy Equipment Life Cycle GHG (Carbon) Emissions (2020-2029) (billions of tons of CO2-eq)
Life Cycle Carbon Emissions in Future Decades. Life cycle carbon emissions can be mitigated and minimized despite the fact they are an unavoidable byproduct of decarbonization investments. Sources of life cycle carbon emissions are diverse and depend on deployment rates. Life cycle emissions from renewable electricity generation and EV battery storage deployment will increase and may then recede when and if demand for new equipment recedes. Life cycle carbon emissions forecasts may become more accurate as experience accumulates. Referring to Table 1 as a baseline, our next step will be to evaluate best and worst case scenarios.
Near Term Life Cycle Carbon Minimization. Life cycle carbon emissions will likely account for a significantly larger share of total GHG emissions in future decades. Minimizing rates of life cycle carbon emissions increases will require action to reduce overall energy intensity, focus on major sources, plan for greater circularity, increase equipment longevity and begin explicitly accounting for and forecasting life cycle carbon emissions as a sub-set of overall energy related emissions.
Energy Intensity. We can reduce energy intensity by adopting policies that reward both energy efficiency and energy conservation. Energy efficiency relies on intelligent control of energy consuming systems and their integration with supply. Heat pumps, for example, can operate more efficiently and incur a smaller carbon debt if solar and geothermal heat is used to reduce the temperature gap over which heat is pumped. There are also ways to lower the gap when heat is pumped for cooling purposes, for example by relying on the thermal mass of a building to stabilize its temperature so that cooling operations can be shifted away from the hottest parts of the day.
Energy conservation requires using more pervasive human intelligence to avoid using energy unnecessarily, for example, heating and cooling unused spaces, producing and purchasing vehicles that are oversized relative to their primary intended use, and failing to minimize leakage and losses in energy transport systems. More effective integration of heat storage with solar arrays and heat pumps, closer attention to integration of renewable heat and renewable hydrogen with renewable electricity, more efficient renewable hydrogen production, and longer lithium ion battery lifetimes will be necessary and require closer technical and policy attention as the energy transition continues.
Major Sources. Table 1 shows that life cycle carbon emissions attributable to leakage of electrification refrigerants and lithium ion battery production are already dominant and increasing. Policies focused on high GWP emissions could, for example, reward recovery of high GWP refrigerant and substitution of lower GWP refrigerants. Policies focused on electric vehicle substitution for gasoline and diesel fueled vehicles could, for example, prioritize high usage vehicles until EV substitution is farther along.
Planning for Circularity. Planning for circular renewable energy economies will emphasize recycling, reusing, re-manufacturing and repurposing materials and equipment. One major benefit will be reduction of life cycle carbon emissions of replacement equipment and systems. A circular renewable electrification economy would encompass solar, wind and stationary battery storage as well as efficient electricity usage equipment. A circular global electric vehicle economy would be supported by environmentally responsible sourcing of battery minerals and high vehicle utilization. There is ample information to support national planning for circularity in these cases. National planning processes will inform state planning and state planning will inform city and county planning.
Increase Equipment Longevity. Other than fugitive natural gas emissions that may decline, and electricity storage and transport losses that may increase, life cycle emissions in other Table 1 categories in future decades will eventually stabilize at levels determined by replacement cycles, residual fossil fuel use, and circularity. Current replacement cycles are less than a decade for EV battery storage, a decade and a half for refrigeration and HVAC equipment, and two or more decades for renewable electricity generation. Battery storage longevity is a major concern, both because new manufacture of new batteries results in life cycle carbon emission and because battery round trip efficiency falls off rapidly toward the end of a battery’s life, increasing life cycle carbon emissions of energy supply related life cycle emission.
Explicitly account for life cycle carbon emissions in GHG inventories and forecasts. Clearly, life cycle carbon is already increasing the cost of global decarbonization while retarding progress. At this time, it is an important but not accurately predictable side-effect of life-saving “decarbonization medicine”. Explicit and complete accounting will motivate both improved accuracy and better informed policy attention.
Questions. What technology and strategy adjustments may become important? To what extent will life cycle carbon emissions off-set the effect of substituting renewable energy for fossil fuel use? What might cause life cycle carbon emissions to escalate or exceed current estimates? What can be done to minimize life cycle carbon emissions? For preliminary answers and related references, click here.